manhole

noun4

1. •
   A hole in the ground used to access the sewers or other underground vaults and installations.

   • The king had scarce ceased to writhe, When hate gave a terrible laugh, Like a manhole opened to Hell. — 1936
2. •
   A hole providing access to the inside of a boiler, tank etc.
3. •
   (informal) The anus of man, in a sexual context.
4. •
   (slang) The vulva or vagina of a trans man.